The present invention relates to a circuit and the method for reproducing a luminance signal compatibly between video cassette recorders(VCR) adopting different video signal recording and reproducing systems. More particularly, the present invention relates to a circuit and method for compatibly reproducing a luminance signal recorded on a video cassette tape by conventional video signal recording and reproducing apparatuses in such a system as is described in detail in the U.S. patent application Ser. No. 07/569,029 on the invention titled "AN IMPROVED VIDEO SIGNAL RECORDING SYSTEM", filed Aug. 17, 1990 by the same Applicant, now U.S. Pat. No. 5,113,262.
Generally, in a conventional video signal recording and reproducing apparatus, as shown in FIG. 1A and FIG. 1B, when a composite video signal is recorded on a video cassette tape, the luminance signal separated in Y/C separator 1 is supplied to an emphasis portion 2, thereby emphasizing the luminance high frequency components. When the composite video signal is reproduced from the video cassette tape, the luminance signal is processed by a de-emphasis portion 10 in order to restore the luminance high frequency components emphasized during recording the video signal to the original signal. This process will be described below with reference to FIG. 1A and FIG. 1B.
Referring to FIG. 1A, if a composite video signal is inputted to a recording circuit of an existing video signal recording and reproducing apparatus which will be referred to as a video cassette tape recorder (hereinafter, a VCR), the composite video signal is separated into the luminance and chrominance signal in Y/C separator 1 and the separated luminance signal is emphasized in an emphasis portion 2. Then, the emphasized luminance signal is supplied to FM modulator 3.
This FM modulated signal in FM modulator 3 is amplified in a record amplifier 4 and recorded by a recording head 5 on a video cassette tape. At this time, although not shown in FIG. 1A, the chrominance signal separated in Y/C separator 1 is processed in a chrominance signal processor, is mixed with the luminance signal, and is recorded.
Referring to FIG. 1B, a reproducing circuit of a conventional VCR reproduces a composite video signal recorded on the video cassette tape through a playback head 6 and supplies the reproduced composite video signal to a standard luminance signal reproducer 7, thereby reproducing the luminance signal. The reproduced luminance signal Y is limited by a limit portion 8 and then demodulated in FM demodulator 9. This demodulated luminance signal is also supplied to a de-emphasis portion 10 in order to restore the luminance signal emphasized in the recording circuit. Then, a composite video signal generator 11 outputs a composite video signal Y+C by mixing the chrominance signal C outputted from a chrominance signal reproducer which is not shown in FIG. 1B, and the de-emphasized luminance signal.
However, as shown in FIG. 2A and FIG. 2B, a recording circuit and a reproducing circuit of an improved video signal recording and reproducing apparatus to which the circuit of the present invention is applied are different from the existing record and playback processing circuits shown in FIG. 1A and FIG. 1B. That is, in the VCR to which the present invention is applied, when a composite video signal is recorded on a video cassette tape, the high frequency luminance signal to be folded passes through an adaptive de-emphasis portion 23 and then is frequency folded. Next, during reproducing the luminance signal is frequency-unfolded and then passes through an adaptive re-emphasis portion 34, This process will be described below with reference to FIGS. 2A and 2B.
Referring to FIG. 2A, a composite video signal Y+C is separated into luminance signal Y and chrominance signal C in Y/C separator 22 via A/D converter 21. This separated luminance signal Y is supplied to an adaptive de-emphasis portion 23. Then, a frequency folding portion 24 receives the de-emphasized signal, and outputs a frequency-folded signal. Next, a frequency folding information recording portion 25 inserts frequency folding information in the horizontal synchronizing signal Hsync in order to separate the folded frequency during the playback processing. Next, this luminance signal on which the frequency folding information is inserted is D/A converted in D/A converter 26, and then is recorded by a recording head 27 on a video cassette tape together with a chrominance signal through sequential processes not shown in FIG. 2A.
Referring to FIG. 2B, a playback processing circuit of an improved video signal recording and reproducing apparatus to which the circuit of the present invention is applied reproduces a luminance signal Y in a standard luminance signal playback portion 29 via a playback head 28. For the purpose of restoring the pre-emphasized luminance signal during the record processing which is not shown in FIG. 2A, the high frequency components of the luminance signals are de-emphasized in a de-emphasis portion 30. The de-emphasized luminance signal is FM demodulated in an FM demodulator not shown in FIG. 2B, and then the FM demodulated luminance signal is inputted to A/D converter 31. Next, a frequency folding information detecting portion 32 receives the A/D converted signal and detects the frequency folding information inserted in the frequency folding information recording portion 25 during the record processing of the video signal.
Next, a frequency unfolding portion 33 unfolds the frequency folded signal in accordance with the frequency folding information detected in the frequency folding information detecting portion 32. This unfolded signal is then restored to the original signal via an adaptive re-emphasis portion 34. D/A converter 35 then receives the restored signal and outputs the desired luminance signal. Next, a composite video signal generator 36 outputs a composite video signal Y+C after mixing a chrominance signal outputted from a chrominance signal processor for processing the reproduced chrominance signal (not shown in FIG. 2B), and the luminance signal.
Thus, when a video signal recorded by a record processing circuit in the existing VCR as shown in FIG. 1A is reproduced by a playback processing circuit in the improved VCR as shown in FIG. 2B, the recorded video signal could not be restored to the original signal during the playback processing because the recorded video signal during the record processing is unfolded in the frequency unfolding portion 33 and then passes through the improved video signal playback process.
Consequently, when the video signal recorded by the existing VCR is reproduced in the system which is disclosed in the aforesaid U.S. patent application No. 07/569,029, the picture quality having the same resolution as that of originally recorded video signal is not obtained, thereby resulting in the problem that perfect compatibility between the different video signal recording and reproducing systems is not maintained.